It is known that a short channel effect, in which a leakage current flows at the time of an off-operation of a transistor, arises in an MISFET (Metal Insulator Silicon Field Effect Transistor), which is one of semiconductor devices, when the gate length thereof is short, and it is known to form an extension region which is shallow than the source/drain regions in order to suppress the short channel effect.
In the formation of such an extension region, it is required to form the depth thereof to be more shallow (e.g. 10 nm or less) in association with the recent further miniaturization of the MISFET. The extension region is generally formed by introducing impurities into a substrate, and after that, by activating the introduced impurities by the thermal processing thereof. For the introduction of the impurities, an ion implantation method of accelerating ions of impurities to inject the ions into a substrate has conventionally been used. In order to form a shallow extension region by the use of the ion implantation method, it is necessary to make the acceleration energy of ions small. If the ions of the impurities desired to be introduced are light, such as boron ions, many accelerated ions have diffused before they reach the substrate when their acceleration energy is made to be small. Consequently, it was difficult to form a shallow extension region by the use of the ion implantation method.
Accordingly, it is known to use a plasma doping method of introducing impurities into a substrate by exposing the substrate to plasma containing the impurities therein that are desired to be introduced, and by applying bias potential to the substrate (see, for example, patent document 1).
In the plasma doping method described in the patent document 1, a phenomenon in which radicals in the plasma deposit on a surface of the substrate and a phenomenon in which ions accelerated by the bias potential are radiated onto the substrate to be drawn into the substrate simultaneously occur. It is needed to deposit the radicals uniformly on the surface of the substrate and to radiate the ions uniformly to the substrate here in order to introduce the impurities uniformly in the substrate by using the plasma doping method. That is, it is necessary to obtain a uniform in-plane distribution of the radicals and a uniform in-plane distribution of ions on the surface of the substrate.
In order to obtain the uniform in-plane distribution of the ions on the surface of the substrate, it is possible to control the plasma by, for example, a magnetic field. However, because the radicals and the ions are different from each other in the existence of electric charges and the like, and because the radicals exist more than the ions in the plasma, the plasma controlled in order to obtain the uniform in-plane distribution on the surface of the substrate does not enable the obtainment of the uniform in-plane distribution of the radicals on the surface of the substrate, and does not enable the uniform deposition of the radicals on the surface of the substrate. As a result, the plasma doping method described in the patent document 1 has a problem of the impossibleness of the uniform introduction of impurities into the substrate because the method cannot simultaneously secure both of the uniform in-plane distributions of the radicals and the ions on the surface of the substrate.
Moreover, the plasma doping method causes a disadvantage of the etching of the surface of the substrate by the ions because the drawing speed of the ions is generally faster than the depositing speed of the radicals in the processing apparatus executing the plasma doping method described in the patent document 1. Consequently, if the plasma doping method described in the patent document 1 is applied to the formation of the extension region, the shallow extension region could be formed, but the surface of the substrate is etched, and consequently the sheet resistance value of the extension region formed in the substrate is high.